Researchers seek to transfer water-wise traits to biofuel crops

By Susanne Retka Schill | October 04, 2012

University of Nevada-Reno researchers are leading an effort to identify the gene pathways responsible for the great water efficiency in desert plants, and transfer that to poplar trees being developed for biofuels.

A five-year, multi-institutional $14.3 million U.S. DOE grant to explore the genetic mechanisms of crassulacean acid metabolism (CAM) and drought tolerance in desert-adapted plants was awarded to a team of researchers including John Cushman, a biochemistry professor at UN-R; Xiaohan Yang at the Oak Ridge National Laboratory; James Hartwell at the University of Liverpool, U.K.; and Anne Borland at Newcastle University, U.K. and ORNL.

Cushman, director of the project, explained the ORNL team has done a great deal of work with the poplar genome along with studying agave, while others on the team have expertise with the other desert species being examined, ice plant and prickly pear cactus. The team will be working to identify the gene pathways involved in these desert species’ ability to use 20 percent of the water typically required by other plants, and transfer those traits to poplar.

The metabolic mechanisms in species that normally perform photosynthesis during the day (known as C3 photosynthesis) will be altered so the plants can take up carbon dioxide at night, when the potential for water loss is lower. This specialized mechanism of nocturnal photosynthesis is known as CAM.

The pores on plant leaf surfaces, called stomata, open and close at certain times of the day to allow water and carbon dioxide to be exchanged. With CAM, the exchange happens mostly at night, when it is cooler and more humid, and then C3 photosynthesis occurs during the day in a more water-wise manner. CAM species can grow and thrive with about 8 to 16 inches of precipitation a year, far less than the 20 to 40 inches per year required for current biofuel feedstocks.

“In order to identify the optimal ‘parts-list’ for introducing CAM-like properties into other plants, we will undertake groundbreaking research on a diverse range of plants that use CAM, with the goal of identifying the key genes and proteins required to make this photosynthetic adaptation work efficiently,” Hartwell said.

“We will introduce changes that enable poplar to take up carbon dioxide at night and subsequently process this carbon during the day while the leaf pores remain closed,” Borland said. “If successful, our research could lead to poplar that requires up to 80 percent less water for biomass production and consequently will be able to grow in more marginal habitats. In the longer term, the technology has the potential to help tackle food security by maintaining the productivity of food crops in the drier and warmer world that climatologists predict for the next 60 years.”

“We’re focusing on poplar due to its fast-growing nature and wide-ranging habitat, which has led to it gaining worldwide recognition as a dedicated feedstock for biomass production; plus poplar has a rich portfolio of genetic and genomics tools and resources,” Yang said. “The relatively low water-use efficiency resulting from C3 photosynthesis in poplar is a limiting factor for sustainable production of poplar tree biomass on marginal land. The biodesign principles and genome-engineering capabilities developed in this project can be extended to increase the water efficiency of other bioenergy and food crops.”

What is learned in transferring desert-adaptations to poplar, if successful, should be transferrable to other crops. The goal isn’t as much to increase yield potential as it is to improve the target crops’ abilities to withstand more extreme weather fluctuations and drought, Cushman said. “With climate change predictions for a 7 degree Fahrenheit (3.8 degree Celsius) increase in temperature and a decrease in reliable precipitation patterns by 2080 for much of America’s breadbasket, and with a greater need for sources of biofuels for transportation, these biodesign approaches to enhancing biomass production become very important,” Cushman said.

The grant, titled “Engineering CAM Photosynthetic Machinery into Bioenergy Crops for Biofuels Production in Marginal Environments,” is funded through the DOE’s Office of Biological and Environmental Research, Genomic Science: Biosystems Design to Enable Next-Generation Biofuels.